A computing system that has multiple processors, each perhaps with different memories and input/output (I/O) bus locality, may be described as heterogeneous. Besides the main central processing unit (CPU), auxiliary processors may be present, such as general purpose CPUs or GPUs, and peripheral processors. Examples of auxiliary processors residing on peripherals include programmable GPUs and those on network controllers. Auxiliary processors may also include general purpose CPUs dedicated to running applications and not running operating system (OS) code. Or, they may include processors to be used in low power scenarios, such as those in certain media capable mobile computers. Conventional peripheral processors typically run domain-constrained applications, but have processing power that might be employed for other tasks.
Other domains to which peripheral processors are targeted include video, network control, storage control, I/O, etc. In a heterogeneous system, the multiple processors may have very different characteristics. Typically, the processors have different instruction set architectures. Peripheral processors that enable ancillary computing functions are often located on physically separate boards in the computing system or are located on the same mainboard as the main CPU, but relatively remote in a logical sense-since they exist in ancillary subsystems. Because peripheral processors often support different instruction set architectures than the general purpose CPUs in the system, they interact with the operating system in a limited manner, through a narrowly defined interface.
The various different auxiliary and peripheral processors (each referred to hereinafter as “auxiliary”) usually constitute resources in a computing system that lie idle at least part of the time, even when the main CPU is intensively processing under heavy load-this is because conventional operating systems do not have enough direct access to the auxiliary processors to delegate application processing tasks that are usually carried out only by the main CPU. Each auxiliary processor, in turn, usually has access to additional local resources, such as peripheral memory, etc. These additional resources also lie idle most of the time with respect to the processing load of the main CPU, because they are not so accessible that the operating system can delegate processing tasks of the main CPU to them in a direct and practical manner.